An investigation is under way after paramedic crews could not attend to a man who suffered a fatal heart attack because they were on "rest breaks".
The man stopped breathing shortly after the ambulance arrived
A rapid-response car was sent when a 999 call was made after the 73-year-old collapsed at the Edmonton Green shopping centre in north London.
But London Ambulance Service (LAS) confirmed the crews were on a break, under EU rules, when the call was made.
An ambulance arrived 20 minutes later but the man died shortly afterwards.
Attempts to resuscitate him in the ambulance and on the way to hospital failed.
A London Ambulance Service spokesperson said: "Having looked at the availability of ambulances in the area during this period, we can confirm that two crews were on a rest break at Edmonton Ambulance Service at the time of the 999 call."
He said there were four other ambulances on duty in the area and available to respond to emergency calls when the second crew was allocated a break at 1257 GMT on December 31.
When the 999 call was received at 1322 GMT, with reports a man had collapsed in the shopping centre, a rapid response car was dispatched.
According to the spokesperson the car arrived at the shopping centre eight minutes later at 1330 GMT and the paramedic immediately started treatment.
An ambulance was then sent at 1332 GMT, after becoming free from a previous incident, and arrived at the centre almost 10 minutes later, at 1341 GMT.
He said it took another "few minutes" to reach the patient.
No other details of the patient have been provided, but it was reported he was 73-years-old and had suffered a heart attack on a betting shop floor.
New arrangements giving ambulance staff a formal rest break during their shift came into effect in December last year, under the European Working Time Directive.
Anyone working a shift between six and 10 hours long is allocated a rest break of 30 minutes.